Plastic and glass containers or bottles are prevalent in a wide variety of shapes and sizes for holding many different types of materials such as detergents, chemicals, motor oil, beverages, etc. These containers are glass or plastic (mono or multi layers) of polyethylene, polypropylene, polyester or vinyl along with other specialty blends for specific barrier and product resistance performance. These containers are typically provided with a label which designates the trade name of the product and may contain other information.
Labels designed to adhere to glass and/or polyethylene terephthalate (PET) are typically applied using a cold or hot glue application processes. During the automated bottle labeling, glue (high viscosity, tacky liquid) is directly applied to the preprinted label and then applied to the bottle. The use of glues, however, requires extensive cleaning as the glue dries and accumulates on the bottling line equipment. In some cases, the glue must be heated prior to application, which requires additional heating equipment and increases energy costs.
In addition to cold- and hot-glue applied labeling methods, preprinted pressure sensitive adhesive (PSA) labels are also used. These labels utilize a release liner to protect the preprinted label face from interacting with the tacky PSA. The use of traditional PSA labels results in several million pounds of liner waste per year in the bottling industry. PSAs also lack removability properties desirable in downstream recycling and bottle reusing facilities.
Attempts to overcome these limitations have been described in the literature. U.S. Pat. Nos. 6,306,242; 6,517,664; and U.S. Pat. No. 6,663,746 to Dronzek describe a labeling system for applying labels to plastic and glass bottles. The labeling system includes applying a layer of a hydrophilic solid material to a polymeric label to form a hydrophilic layer on the polymeric label; applying water, water containing a cross-linking agent or a water based adhesive over the hydrophilic layer to form a fastenable polymeric label; fastening the fastenable polymeric label to a glass, plastic or metal container or surface; and curing the polymeric label on the glass, plastic or metal surface or container.
U.S. Pat. No. 7,943,714 to Schneiders describes a labeling system containing a blend of two or more polymers having different hydrophilicities or using a polymer with repeat units having carboxylic, sulfonic or phosphonic acid groups and/or their salts.
Dronzek and Schneiders require the use of non-porous or relatively non-porous face sheets, such as polypropylene, high/low density polyethylene, polyethylene terephthalate, polystyrene, polycarbonate, vinyl and compatibilized blends. Face sheets prepared from these materials typically have a moisture vapor transmission rate of less than about 150 g/m2/24 hr as measured using the TAPPI T448 om-09 standard protocol. In fact, Schneiders discloses that the use of porous face sheets, i.e., those having high moisture vapor transmission rates (MVTR) values, with pressure sensitive adhesives is undesirable because the finished labels exhibit poor wet tack and swimming. Similar disadvantages are described in Dronzek.
Another challenge with PSAs is their application to substrates that are cold and/or wet. PSAs need an initial adhesion or tack to a substrate, followed by the application of pressure to increase the level of the initial adhesion. However, cold temperatures cause PSAs to become firm thereby losing initial tack, and a wet surface prevents the PSA from attaching due to repression of the tack, causing the label to slide off its point of application. Substrates that are cold and/or wet are frequently encountered in the bottling industry where beverages poured into a bottle are cold, causing the bottle to also become cold, and wet due to condensation.
There is a need for labels, particularly for face sheets with high MVTR values that can be applied to a substrate such as glass or PET at variable temperatures and humidity levels. Further, there exists a need for a liner-free labeling system for glass and polyethylene terephthalate (PET) automated bottle labeling applications that provides both quick tack when surfaces are wet and long term label-to-bottle adhesion when dry.
Therefore, it is an object of the invention to provide improved labels that are able adhere to a substrate at a variety of temperatures and/or humidity levels.
It is a further object of the invention to provide improved compositions for adhering labels to a surface at a variety of temperatures and/or humidity levels.
It is yet a further object of the invention to provide improved methods for applying a liner-free label to a substrate.